Centrifugal pump



' Nov. 1'2, 1970 R. A. GREENE 3,541,607

CENTRIFUGAL PUMP Filed May 29, 1968 v I 3 Sheets-Sheet 1 Q Q q mun m m nl l f i l Ill] a Q Pie/02AM F 5 3 1 /9/09 ART IN VI-TNTOR.

el. GEL-6M5 Nov. 17, 1970 a. A. GREENE 3,541,607

GENTRIFUGAL PUMP Filed May 29, 1968 3 Sheets-Sheet 2 Nov. 17, 1970 R. A. GREENE 7 3,541,507

CENTRIFUGAL PUMP Filed May 29, 1968 3 Sheets-Sheet 5 United States Patent 3,541,607 CENTRIFUGAL PUMP Robert Raymond Greene, Chicago, Ill., assignor to International Telephone and Telegraph Corporation, New York, N.Y., a corporation of Delaware Filed May 29, 1968, Ser. No. 732,978 Int. Cl. F0411 1/00, 29/18, 29/00 US. Cl. 415-112 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates in general to centrifugal pumps and in particular to new and improved pump drive shaft seal lubricating and heat transfer arrangements.

Properly lubricating and disposing of the heat generated by pump drive shaft seals has always been a problem affecting the reliability and longevity of centrifugal pumps. The lubrication and related heat disposal problem is especially severe in the relatively small, high velocity, domestic hot water systems.

In the single eye impeller type of centrifugal pumps usually used in these domestic systems, there was a tendency for the entrained gases to collect around the seal surfaces due to the centrifugal and centripetal action of the pump upon the liquid and gases being pumped. Accordingly, the action of the pump caused a pressure gradient in the seal cavity. The pressure is a maximum at the outer periphery of the impeller and a minimum at the pump drive shaft. More specifically, the relatively low mass of the gases mixed into the liquid passing through the pump caused the gases to move out of the liquid stream and into the low pressure area. Because of its reatively high mass, the liquid tends to move toward the outer periphery of the impeller.

As a result of these tendencies, the pump seal becomes surrounded by gas rather than by the liquid being pumped. Hence, the prior art pumps operated without proper lubrication. With no efficient heat conductor contiguous with the pump drive shaft seal, the seal wore out too soon.

These and other problems were solved by a device shown in a US. Pat. 3,340,813 entitled Centrifugal Pumps, granted to Jack Keyes on Sept. 12, 1967, and assigned to the assignee of this invention. When it was introduced to the market, the Keyes invention was an instantaneous commercial success. However, as successful as it was, there has remained room for improvement. For example, the construction shown in the Keyes patent was comparatively expensive, involving four pieceparts spotwelded together and entailing a large amount of manufacturing processing. The Keyes impeller tended to experience some balancing problems, was sometimes attacked by the liquid being pumped, and required more power than is really necessary.

Accordingly, an object of the present invention is to provide a new and improved impeller for centrifugal pumps. In particular, an object is to overcome all of the faults of the Keyes impeller without sacrificing any of its advantages.

3,541,607 Patented Nov. 17, 1970 ice More specifically, an object of this invention is to provide lower cost, lighter weight, better balanced impellers with seals which are properly lubricated.

A related object of this invention is to provide lower cost impellers having positive and continuous flow of fluid through the seal cavity and contiguous to the seal itself.

Yet another object of the invention is to prevent the formation of gaseous insulting pockets around the drive shaft seal.

In accordance with one embodiment of the invention, the impeller is made from tWo simple, molded pieceparts. A front shroud has a double blade set of vanes fixedly mounted thereon. A rear shroud has inlet ports feeding into the spaces :between the double blades. By simply mounting the two parts on a keyed shaft, they may be fitted together to form an impeller assembly of a centrifugal pump in such a way that the liquid and gas mixture are not separated in the seal cavity, but are positively pumped over the seal surfaces. Thus, the seal is lubricated at all times. This arrangement makes it possible to fabricate lower cost impellers that are quieter and longer lived, lighter weight, and better balanced, than the impellers made by the Keyes type of fabrication.

The above mentioned and other objects and features of the invention will become apparent during the course of the following description of the drawing made in conjunction with the following drawings, whcerein:

FIG. 1 is a cross-sectional view taken through a single eye Keyes type impeller centrifugal pump;

FIG. 2 is a sectional view of the Keyes impeller of FIG. 1 showing both the front and rear shrouds;

FIG. 3 is a front plan view of the Keyes impeller assembly of FIG. 2;

FIG. 3a is a section view showing the passageway formed by the rear of the impeller blade and the rear shroud;

FIG. 4 is a sectional view of the Keyes impeller blade without the shrouds;

FIG. 5 is a front plan view of the Keyes impeller of FIG. 4 and of the rear shroud which is used to form a passageway.

FIG. 6 is a perspective view of the inventive impeller improvement over the Keyes impeller shown in FIGS. 1-5;

FIG. 7 is a perspective view of one piecepart including the front shroud with the double blade impeller;

FIG. 8 is a perspective view of the other piecepart including the rear shroud with the shaft seal lubricating inlet ports; and

FIG. 9 is a rear plan view showing how the parts of FIGS. 7, 8 fit together to provide a double suction im peller for both pumping a liquid and degassing a seal.

FIGS. l-S are a photocopy of the drawing in the Keyes patent. These figures and the accompanying description are thought desirable since a full understanding of the Keyes invention is necessary for an appreciation of the improvements made by the subject invention. However, since the Keyes patent is available for further study, the description of FIGS. l-S will be brief.

A single eye impeller, volute type centrifugal pump 11 is shown in FIG. 1. The pump includes a casing 12 having a suction inlet 13 coupled to an eye 15 of impeller assembly 16 by a suction passage 14. The impeller assembly 16 includes hub 17 which is keyed to a rotatable drive shaft 18 and secured by nut 19. The drive shaft 18 is turned by an electric motor (not shown), but secured to a coupling bracket 20. The drive shaft 18 extends through the seal plate 21 which is the back wall of the volute casing 12 having a seal cavity A formed therein.

The coil spring 23 is compressed to exert a force against a cavity seal ring 24.

The impeller assembly 16 draws fluid through the suction passage 14, the eye 15, and forces it out through the discharge passage 27 and discharge outlet 28. To do this, the impeller assembly (FIGS. 2 and 3) has a front shroud 35 shaped to conform to the fluid flow lines and to fit into the eye 15 formed by the seal plate wall structure 21a (FIG. 1). A rear shroud 38 is juxtaposed to and encloses the rear of the impeller blade 36 so as to form a fluid passageway 39. Fluid coming into the eye is forced to travel through the space B between the front shroud and the impeller blades 36.

Another section 38b of the rear shroud 38 surrounds the seal assembly to form a fluid passageway 39. The fluid in the seal cavity A is circulated through passageway 39a, contiguously to the seal, and then pumped through passageway 39 (as indicated by arrows c in FIGS. 1 and 3) and into the volute discharge passage 27. The rear shroud 38 is designed to force the fluid in the seal cavity A over the seal 24-26 to lubricate it, carry along any gases around the drive shaft, and remove heat generated by the friction between seal 24 and insert 26.

FIGS. 4 and 5 show the impeller 36 as having five equally spaced blades. The major pumping action occurs when the fluid trapped in area B between the blades is pushed outwardly by centrifugal forces. The trapped fluid gains pressure due to the centrifugal force applied thereto by the rotation of the impeller. Some fluid leaks past the impeller into the seal cavity A (as shown by arrows c), and is pulled through passageway 39 into the main discharge passage 27. The velocity of the fluid in this secondary path is governed by such things as the clearance between the shroud 38 and the seal assembly.

The rear shroud arrangement thus forces the fluid over the seal assembly to properly lubricate the seal and remove the friction generated heat. When no rear shroud is provided, the seal assembly is surrounded by escaped gases. Thus, due to the lack of lubrication between the rotating seal 24 and the stationary insert 26, friction increases between the seal and insert. The increased friction generates detrimental heat, causes excessive wear of the seal and consequently increased pump wear and down time, as well as noisy operation of the pump.

The Keyes invention described thus far involves four pieceparts: front shroud 35, blade 36, rear shroud 38, and hub assembly 17. The parts 35, 36, 38 are spotwelded together, as at 40. The journal in hub 17 must be machined. Therefore, this is a comparatively expensive assembly. The resulting structure is subject to manufacturing tolerances so that the impeller is not always in good balance. The four pieceparts are steel, thus the impeller is heavy and requires relatively large amounts of power. It is subject to rusting or otherwise being attacked by the pumped fluid. The steel is an elastic material which both generates and transmits sound to make a noisy assembly.

The present invention overcomes these and other problems through a use of two simple pieceparts which may be made by an injection molding process from a lightweight, homogeneous plastic (such as one sold 'under the trade name Oleform, an asbestos filled polypropylene material) which withstands extremely high temperature. The mold may be made with great precision so that the resulting impeller is finely balanced and the hub journal is automatically a smooth, precise fit, completely free of all wobble and play. The two pieceparts fit together in perfect alignment owing to the precise molding and an alignment of key slots in the hubs of the two units.

In greater detail, the inventive impeller includes front and rear pieceparts 50 (FIG. 7) and 51 (FIG. 8) which fit together as shown in FIG. 6. Fluid enters the pump at 52, is swirled between front and rear shrouds 53, 54 and hurled outwardly by centrifugal force, as at 55, for example. The swirling results from a rotation of double blade vanes (such as 56) which separates the fluid into five moving streams, in a manner which should become more apparent from a study of FIG. 6.

In greater detail, the front piecepart includes the shroud 53 terminating at one end in an upstanding collar 58 which fits into the eye of the pump and at the other end in the periphery of a flared skirt. The flared skirt shape generally matches the smooth and even streamlines of a flowing fluid traveling at the pumped velocity. Upstanding on the underside and molded as an integral part of front shroud 50 are five (in this example) double bladed vanes 56, 60-63. Each of the blades also follows the smooth contours of the flared skirt 53. The two blades of each pair of vanes are spaced apart by a narrow distance, as shown at 65. The spaces between the double blades are .the same as the duct 39 (FIG. 3) used to carry the lubricating and cooling current represented by the arrows c in the various figures.

The rear piecepart 51 (FIG. 8) includes the rear shroud 54 having a hub section 70 connected to a flared skirt 54 having contours which match the contours of the skirt 53, of FIG. 7. A collar 71 is dependent from the shroud 54 to form the general shape of the skirt 38b (FIG. 2). A spider 72 centers the hub 70 in the shroud 54 and forms a number of passageways through which the lubricating flow 0 may travel. The spider 72 is recessed into the shroud 54 by a distance 74.

The front shroud 53 also has a center hub 75 connected to the flared skirt by a spider formed from the double bladed vanes 56, 60-65. The spider can be seen at 76 in FIG. 6. The spaces between the spider arms form five ducts, as at 77, through which the major stream fiows into and out of the impeller. The hub 75 on the front piecepart stands out, away from the vanes 56, -63 by a distance 78 (FIG. 7) which is equal to the recessed distance 74 on the piecepart 51. Thus, when the two hubs 70, 75 are fitted onto the same shaft, the piecepart 51 nestingly receives the piecepart 50 to help stabilize the mechanical fit. To help align the parts, each hub includes a key slot 80, 81.

By comparing FIGS. 1, 6, 7, 8, it should be apparent that the total impeller unit FIG. 6 may be made by placing the rear shroud piecepart 51 and then the front shroud piecepart 50 on shaft 18 with the key slots 80, 81 aligned. Then the nut 19 is tightened on threaded end of shaft 18 to hold the parts 50, 51 in place.

The operation of the double suction impeller should now be clear. As the entire unit is rotated by a motor acting on shaft 18, the fluid 52 being pumped enters the eye 15 of the pump, travels through the five ducts (such as 77) formed by the spider 76 on the front piecepart 50, and is expelled between the vanes 56, 60-63 (as at 55, for example). This is the first suction formed by the impeller.

The second suction is formed by the flow indicated by the arrows c. Thus, in FIG. 6, a small part of the main stream 55, leaks around skirt 54, is pulled around behind the collar 71, and then pulled up into the space between each pair of blades forming the double blade fins 56, 60-63. In the back view (FIG. 9 and in FIG. 3a), a small x-mark c1 represents the tail feathers of arrows 0 indicating that the fluid flow through the ducts formed by the spider 72. These curernts c flow upwardly into space 65 between the double blades, and out over the rear shroud 54, as indicated in FIG. 8. As shown in FIG. 7, these currents c flow in between the double blade and emerge to join the mainstream represented by the arrows such as 55. To help identify the passageway for the secondary flow of arrows c, one exemplary passage is shown (FIG. 9) by crosshatching between dot-dashed lines representing the double blade vanes 56. The intakes for other similar channels between the double blades are shown as crosshatched in FIG. 9. These intakes are molded into the hub area of the front piecepart 50.

The operation and advantages of the invention should now be clear. First, the inventive impeller is much less expensive and much easier to make. The mold for forming the pieceparts may be made with far greater precision than would be possible with the stamped pieceparts of the original Keyes design, FIGS. 1-5. Thus the impeller is better balanced. Finally, the plastic material is homogeneous, lightweight, and immune from attack by the liquid being pumped.

While the principles of the invention have been described above in connection with specific apparatus and applications, it is to be understood that this description is made only by way of example and not as a limitation on the scope of the invention.

I claim:

1. A double suction shaft mounted impeller comprising only a front and rear pieceparts molded from a lightweight, homogeneous material, the front piecepart comprising a shroud terminated at one end in an upstanding collar and at the other end in a flared skirt,

a plurality of double bladed vanes molded into said front shroud,

a hub part held by the inner ends of said vanes and forming a plurality of ducts between the double bladed vanes for receiving the main current flow of material pumped by the impeller, V

the rear piecepart including a skirt like surface extending across the face of the double bladed vanes and comprising rear shroud means for completing a first set of ducts between said double bladed vanes and a second set of ducts, each of said second set of ducts being formed between the blades of said doubled bladed vanes,

said second set of ducts communicating with the fluid about the rear shroud piece and adapted to pull a material being pumped from said first set of ducts around the rear piecepart and up into said second set of ducts, the flow through said first and second ducts merging at the outlets thereof, and

said rear shroud means extending axially rearwardly and adapted to provide a leakage path between said shroud and a sealing means for said shaft, thereby assuring fluid flow past said sealing means.

2. The impeller of claim 1 wherein the flow through said second ducts comprises means for lubricating and cooling said hub area.

3. The impeller of claim 1 wherein the flow through said second ducts comprises means for degassing said fluids about the shaft.

4. The impeller of claim 1 wherein said first piecepart comprises the eye of a single eye impeller, and housing 6 means surrounding said impeller and forming a volute type centrifugal pump.

5. The assembly of claim 1 and a housing having a liquid inlet, a suction passage, a pressure chamber, and a liquid outlet, said chamber including a sealing chamber communicating around said shroud to said pressure chamber, and a seal ring around a shaft in said sealing chamber, said secondary stream flowing from said pres sure chamber to said sealing chamber and into the space between said double blades.

6. An impeller assembly for mounting on a pump shaft,

said assembly comprising only a separately molded front shroud art, a separately molded rear shroud part generally complementary to said front shroud part,

each of said shroud parts comprising a centrally located hub,

spider means forming inlet ducts for fluid pumped by said impeller assembly joining each of said hubs to the front and rear shroud parts respectively,

the centrally located hub of said front shroud part extending rearwardly from the rest of the front shroud part, the centrally located hub of said rear shroud part being indented at the front thereof to nestingly receive the hub portion and said front shroud part,

said shroud parts being spaced apart by double blade vanes unitary with said front shroud part,

said double blade vanes and said inlet ducts being adjoined and shaped to pump a first main stream of fluid from an eye on one side of said impeller and outwardly between both of said shroud parts toward the periphery of said shroud parts, and

a secondary stream of fluid from the rear side of said impeller between said rear shroud and said shaft and outwardly between said double blades toward the periphery of said shrouds.

7. The assembly of claim 6 wherein each of said hubs includes a key slot, and

a complementary key slot on said shaft for aligning said front shroud part and said rear shroud part.

References Cited UNITED STATES PATENTS 2,219,390 10/1940 Iacobsen 103-115 2,358,744 9/1944 Stepanotf 103-115 3,285,187 11/1966 Anderson 103l15 2,710,580 6/1955 Holzworth 103115 2,766,699 10/1956 Bayless 103l15 HENRY F. RADUAZO, Primary Examiner US. Cl. X.R. 

